The present invention relates to balloon cannulas, and in particular to auto-inflate retrograde cannulas used in the delivery of cardioplegia.
Retrograde cannulas are commonly employed during certain cardiac surgical procedures, in order to deliver cardioplegia (CPG) into coronary veins to effect cardiac arrest of a patient by depolarizing cell membranes of the heart tissue (see U.S. Pat. No. 5,395,331).
In order to occlude the coronary sinus, the distal end of the cannula includes an inflatable balloon which, when inflated, seals against a wall of the coronary sinus. Balloons may be of the manual-inflating or auto-inflating type. In a manual-inflating type, a surgeon inflates the balloon by injecting a set amount (volume) of fluid therein. However, there exists a risk of over-inflation of the balloon, which can damage the coronary sinus.
The present invention pertains to the auto-inflating type (also referred to as self-inflating), wherein the balloon is in fluid communication with an infusion lumen of the cannula and is thus inflated by pressurized CPG being delivered to the heart. Thus, the risk of overinflation does not exist because the balloon is inflated to a pressure rather than to a volume as in the case of a manual-inflate balloon.
It will be apparent that the balloon of an auto-inflate cannula becomes deflated when the delivery of CPG is stopped. The cannula may thereafter be kept in place during the surgery in order to be able to periodically administer additional CPG. However, when the balloon becomes deflated, the distal end of the cannula may undergo unwanted displacement. This does not occur in the case of a manual-inflate cannula, but there occurs therein the risk of overinflation as described above.
Although it is common to affix the cannula in place by suturing the cannula to adjacent body tissue, the sutures are placed behind the balloon and thus are spaced by a few inches from the distal tip of the cannula. Thus, the portion of the cannula disposed ahead of the sutures may tend to shift. Such a tendency to shift is more prevalent during the delivery of warm CPG (and shiftable) than cold CPG, because the cannula is made more pliant by the warm CPG.
Since the ability of the distal end of the cannula to become displaced results from the deflation of the balloon, it would be desirable to enable the balloon of an auto-inflate retrograde balloon to stay inflated even when fluid is not being delivered through the cannula.